The statements in this section merely provide background information related to the present disclosure and are not admitted as prior art.
Moving Picture Experts Group (MPEG) and Video Coding Experts Group (VCEG) have developed a new standard of video compression technology that is superior to the existing MPEG-4 Part 2 and H.263 standards. The new standard is called H.264/AVC (Advanced Video Coding) and was jointly announced as MPEG-4 Part 10 AVC and ITU-T Recommendation H.264. H.264/AVC (hereinafter, simply referred to as H.264) has significantly improved picture quality and performance by using various encoding methods. In addition, new standardization for higher picture quality than high-definition (HD) is under discussion by Joint Collaborative Team on Video Coding, the joint team of MPEG and VCEG.
As the existing moving picture encoding methods, an intra prediction encoding method and an inter prediction encoding method have been used. The intra prediction encoding method predicts a block by using a prediction value from a block encoded within a frame being currently encoded. The inter prediction encoding method predicts a block of a current frame by estimating a motion from a previously reconstructed frame.
In the intra prediction method for a luma signal, an intra 4×4 prediction, intra 16×16 prediction and intra 8×8 prediction have been used according to a prediction direction and the size of a block to be encoded.
FIG. 1 is a diagram of nine 4×4 intra prediction modes.
Referring to FIG. 1, the intra 4×4 prediction includes nine prediction modes: a vertical mode, a horizontal mode, a direct current (DC) mode, a diagonal down-left mode, a diagonal down-right mode, a vertical-right mode, a horizontal-down mode, a vertical-left mode and a horizontal-up mode.
FIG. 2 is a diagram of four 16×16 intra prediction modes.
Referring to FIG. 2, the intra 16×16 intra prediction includes four prediction modes: a vertical mode, a horizontal mode, a DC mode and a plane mode. Similarly to the intra 16×16 prediction, the intra 8×8 prediction also includes four prediction modes.
The inventor(s) has noted that in an inter prediction method (inter predictive coding) for a video having a 4:2:0 video format, motion compensation has been used. Specifically, a video frame is divided, and a current block is predicted by estimating a motion from a previously encoded frame. The inventor(s) has experienced that when the block size of motion compensation is reduced for use, a current block can be predicted with higher accuracy. However, the inventor(s) has noted that the requirement to encode motion vector information for each block results in an increase in the amount of code being encoded. The inventor(s) has noted that in addition, when the motion compensation is performed, a more accurate motion vector is obtained by looking into not only motion vectors in integer samples having integer pixels but also in sub-samples having a ¼ sample resolution with respect to a luma component and a ⅛ sample resolution with respect to a chroma component. However, the inventor(s) has experienced that since luma and chroma samples of sub-sample positions do not exist within a reference picture, generating these values by interpolating neighboring samples in the reference picture is required.